The present invention relates to a method for forming a sieve material by thickening a previously formed electrically conductive sieve skeleton by metal deposition in an electrolysis bath until the final thickness of the sieve material has been reached, one or more chemical compound(s) being present in the electrolysis bath used for the metal deposition having the properties of a second-class brightening agent.
Such a method is disclosed by EP-B1-0 038 104.
Said publication describes how a sieve skeleton is formed on a suitable matrix by electrolytic metal deposition. Said sieve skeleton is removed from the matrix and is thickened in an electrolytic metal deposition bath until a desired final thickness has been reached. During the thickening of the metal sieve skeleton, a chemical compound which has properties of a second-class brightening agent is present in the bath. For a description of such chemical compounds, reference is made to Modern Electroplating; 3rd edition John Wiley & Sons; 1973; page 296 et seq, and in particular, page 302 et seq.
The patent publication cited above describes how a less rapid closure by growth of the perforations in the sieve skeleton occurs in the presence of a chemical compound which has the properties of a second-class brightening agent since a preferred growth direction can be observed which is perpendicular to the plane of the sieve skeleton. In other words, in the presence of a chemical compound having properties of brightening agent of the second class, the sieve skeleton will exhibit less growth in the plane of the sieve skeleton (with reduction in size of the perforations) and more growth in the direction perpendicular to the plane of the sieve skeleton. On-checking, growth ratios of greater than 1.5 are observed. That is to say, the largest total growth perpendicular to the plane of the sieve skeleton is 1.5 times as great as the largest total lateral growth of a crosspiece in the plane of the sieve skeleton.
In view of the desired properties during the later use of the sieve material, it is often advisable to subject the thickened sieve skeleton material to an annealing treatment by heating said material under controlled conditions.
Such an annealing treatment is disadvantageous because it employs an additional treatment under controlled conditions and the Applicant has therefore searched for a method with which the need for such an annealing treatment is superfluous.